JP3645465B2 - Display device - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an active display device, and more particularly to an active liquid crystal display device, in which a clear gradation level can be set.
[0002]
[Prior art]
The liquid crystal composition has different dielectric constants in the horizontal and vertical directions with respect to the molecular axis due to its material properties, so it can be easily aligned horizontally or vertically with respect to an external electric field. it can. The liquid crystal electro-optical device performs ON / OFF display by controlling the amount of transmitted light or the amount of dispersion using the anisotropy of the dielectric constant.
[0003]
FIG. 2 shows the electro-optical characteristics of the nematic liquid crystal. When the applied voltage is Va (A point 201), the transmitted light amount is approximately 0%, Vb (B point 202) is about 20%, Vc (C point 203) is about 70%, Vd ( In the case of D point 204), it becomes about 100%. In other words, if only the points A and D are used, black and white two-tone display can be performed, and if the rising portion of the electro-optical characteristics such as points B and C is used, intermediate gray-scale display can be performed.
[0004]
[Problems to be solved by the invention]
In the case of gradation display of a liquid crystal electro-optical device using a conventional TFT, gradation display is performed by adjusting the voltage in an analog manner by changing the gate applied voltage of the TFT or the applied voltage between the source and drain.
[0005]
However, it is difficult to make all of the many TFT elements having a matrix configuration so as to have uniform electrical characteristics, and since there are large variations, fine adjustment of the intermediate voltage particularly necessary for analog gradation display is not possible. It was very difficult.
[0006]
As another method for performing gradation display, a method for performing digital gradation display in accordance with the ON / OFF ratio using, for example, 16 frames using a plurality of writing (display frames) is proposed. It had been. In this case, when 16 frames are turned on and 8 frames are turned off, and the remaining 8 frames are turned off, gradation display is performed with an average transmittance of 50%. In addition, when 4 frames of the 16 frames are ON and the remaining 12 frames are OFF, gradation display is performed with an average transmittance of 25% transmission. However, when this method is used, there is a high possibility of interrupting the minimum number of confirmation frames corresponding to 30 frames, which is a frame that cannot be confirmed by human eyes, which has been a factor of degrading display quality.
[0007]
[Means for solving problems]
Therefore, the present invention proposes means for supplying a clear gradation display level to the liquid crystal by performing digital gradation display instead of the conventional analog gradation display. In the present invention, in the method according to the present invention in which the drive frequency of the driver IC is increased to perform gradation display, gradation display is possible without lowering the substantial frame frequency as in the drive method. Without interrupting the visual confirmation frequency, it is possible to provide a high-quality screen that does not deteriorate the display quality.
[0008]
In the present invention, in the active matrix liquid crystal display device, gradation display of a display device using a display driving method having a display timing related to a unit time t for writing to an arbitrary pixel and a time F for writing one screen is described above. Without changing the time F, the signal during the writing time of the time t is time-divided, and gradation according to the division ratio can be displayed.
[0009]
For the description, a 2 × 2 matrix as shown in FIG. 3 is used. In the case of a conventional display device, as shown in FIG. 4, the electric field applied to the pixel electrode is determined as an average voltage of 16 frames by turning the pixels on and off using, for example, 16 frames. Thereby, the transmittance of the liquid crystal is determined.
[0010]
In the present invention, instead of performing conventional analog gradation control or multi-frame gradation display, as shown in FIG. 1, the signal during the writing time of the unit time t225 for writing to an arbitrary pixel is set as time division. It is possible to display gradations for the number of divisions.
[0011]
At that time, when the electric field changes 227 and 229 in the writing time change as shown in FIG. 1, the liquid crystal operates at the average value of the applied voltage, and clear gradation display becomes possible. Further detailed description will be given below with examples.
[0012]
【Example】
Embodiment 1 In this embodiment, a liquid crystal display device will be described using a liquid crystal display device having a circuit configuration as shown in FIG. An arrangement configuration of actual electrodes and the like corresponding to this circuit configuration is shown in FIG. In order to simplify the explanation, only the portion corresponding to 2 × 2 is shown. The actual drive signal waveform is shown in FIG. In order to simplify the description, the description will be given with the signal waveform in the case of a 2 × 2 matrix configuration.
[0013]
First, a method for manufacturing a substrate for a liquid crystal display device used in this embodiment will be described with reference to FIGS. In FIG. 6A, a silicon oxide film as a blocking layer 51 is formed on a glass 50 such as quartz glass that can withstand heat treatment at an inexpensive temperature of 700 ° C. or less, for example, about 600 ° C., using a magnetron RF (radio frequency) sputtering method. Fabricate to a thickness of ~ 3000 mm. The process conditions were an oxygen 100% atmosphere, a film forming temperature of 150 ° C., an output of 400 to 800 W, and a pressure of 0.5 Pa. The film formation rate using quartz or single crystal silicon for the target was 30 to 100 cm / min.
[0014]
A silicon film was formed thereon by LPCVD (low pressure vapor phase) method, sputtering method or plasma CVD method. When forming by a low pressure vapor phase method, disilane (Si ₂ H ₆ ) or trisilane (Si ₃ H ₈ ) is supplied to a CVD apparatus at 450 to 550 ° C., for example, 530 ° C., which is 100 to 200 ° C. lower than the crystallization temperature. A film was formed. The pressure in the reactor was 30 to 300 Pa. The film formation rate was 50 to 250 cm / min. Boron may be added during film formation at a concentration of 1 × 10 ¹⁵ to 1 × 10 ¹⁸ cm ⁻³ using diborane to control the threshold voltage (Vth) of PTFT and NTFT to be approximately the same. .
[0015]
When the sputtering method was used, the back pressure before sputtering was set to 1 × 10 ⁻⁵ Pa or less, the target was single crystal silicon, and the atmosphere was mixed with 20 to 80% hydrogen in argon. For example, 20% argon and 80% hydrogen. The film forming temperature was 150 ° C., the frequency was 13.56 MHz, the sputtering output was 400 to 800 W, and the pressure was 0.5 Pa.
[0016]
When the silicon film is formed by the plasma CVD method, the temperature is, for example, 300 ° C., and monosilane (SiH ₄ ) or disilane (Si ₂ H ₆ ) is used. These were introduced into a PCVD apparatus, and a high frequency power of 13.56 MHz was applied to form a film.
[0017]
The film formed by these methods preferably has oxygen of 5 × 10 ²¹ cm ⁻³ or less. When this oxygen concentration is high, it is difficult to crystallize, and the thermal annealing temperature must be increased or the thermal annealing time must be increased. On the other hand, if the amount is too small, the leak current in the off state increases due to the backlight. Therefore, the range is 4 × 10 ¹⁹ to 4 × 10 ²¹ cm ⁻³ . Hydrogen was 4 × 10 ²⁰ cm ⁻³ , and compared with silicon 4 × 10 ²² cm ⁻³ , it was 1 atomic%. Further, in order to further promote crystallization with respect to the source and drain, the oxygen concentration is set to 7 × 10 ¹⁹ cm ⁻³ or less, preferably 1 × 10 ¹⁹ cm ⁻³ or less, and the channel formation region of the TFT constituting the pixel is formed. In addition, oxygen may be added so as to be 5 × 10 ^{20 to} 5 × 10 ²¹ cm ⁻³ by ion implantation. At that time, since light is not irradiated to the TFTs constituting the peripheral circuit, it is effective to operate at a high frequency to reduce the mixing of oxygen and provide a higher carrier mobility.
[0018]
After the amorphous silicon film is formed to a thickness of 500 to 5000 mm, for example, 1500 mm by the above method, it is heated at a temperature of 450 to 700 ° C. for 12 to 70 hours in a non-oxide atmosphere, for example, a hydrogen atmosphere. It was held at a temperature of 600 ° C. below. Since an amorphous silicon oxide film is formed on the surface of the substrate under the silicon film, the specific nucleus does not exist in this heat treatment, and the whole is annealed uniformly. That is, it has an amorphous structure during film formation, and hydrogen is merely mixed.
[0019]
By annealing, the silicon film shifts from an amorphous structure to a highly ordered state, and a part thereof exhibits a crystalline state. In particular, a region having a relatively high order in a state after the film formation of silicon is particularly crystallized and tends to be in a crystalline state. However, since silicon is present between these regions, the silicon atoms pull each other. When measured by laser Raman spectroscopy, a peak shifted to a lower wave number side than the peak 522 cm ⁻¹ of single crystal silicon is observed. The apparent grain size is calculated from the half-value width, which is 50 to 500 mm, like a microcrystal, but in reality, there are many regions with high crystallinity and a cluster structure. A film with a semi-amorphous structure in which silicon is bonded (anchored) can be formed.
[0020]
As a result, the coating film exhibits a state that it may be said that there is substantially no grain boundary (hereinafter referred to as GB). Since the carriers can easily move to each other through the anchored portions between the clusters, the carrier mobility is higher than that of polycrystalline silicon in which the so-called GB is clearly present. That is, hole mobility (μh) = 10 to ²⁰⁰ cm ² / VSec and electron mobility (μe) = 15 to 300 cm ² / VSec are obtained.
[0021]
On the other hand, when the film is polycrystallized by high temperature annealing at 900 to 1200 ° C. instead of annealing at the medium temperature as described above, segregation of impurities in the film occurs due to solid phase growth from the nucleus, resulting in GB. Has a large amount of impurities such as oxygen, carbon, nitrogen, and the mobility in the crystal is large, but it creates a barrier in the GB and inhibits the movement of carriers there. As a result, it is difficult to obtain a mobility of 10 cm ² / Vsec or more. That is, in this embodiment, a silicon semiconductor having a semi-amorphous or semi-crystal structure is used for such reasons. However, other semiconductor materials can be used as long as they have high mobility and crystallinity. It is.
[0022]
In FIG. 6A, the silicon film is photoetched with the first photomask (1), and the PTFT region 13 (channel width 20 μm) is formed on the left side of the drawing, and the NTFT region 22 is formed on the right side. did.
[0023]
On this, a silicon oxide film was formed as a gate insulating film to a thickness of 500 to 2000 mm, for example 1000 mm. This was performed under the same conditions as the production of the silicon oxide film as the blocking layer. During the film formation, a small amount of fluorine may be added to fix sodium ions.
[0024]
Thereafter, a silicon film having a phosphorus concentration of 1 to 5 × 10 ²¹ cm ^{−3 on} the upper side, or a multilayer of this silicon film and molybdenum (Mo), tungsten (W), MoSi ₂ or WSi ₂ thereon. A film was formed. This was patterned with a second photomask (2) to obtain FIG. 6 (B). A gate electrode 9 for PTFT and a gate electrode 21 for NTFT were formed. For example, the channel length was 10 μm, the gate electrode was formed with a thickness of 0.2 μm of phosphorus-silicon, and molybdenum was formed thereon with a thickness of 0.3 μm. In FIG. 6C, a photoresist 57 is formed using a photomask (3), and phosphorus is applied to the source 18 drain 20 for NTFT at a dose of 1 to 5 × 10 ¹⁵ cm ^−2. By ion implantation. Next, as shown in FIG. 6D, a photoresist 61 was formed using a photomask (4). Boron was added by ion implantation at a dose of 1 to 5 × 10 ¹⁵ cm ⁻² as a source 10 and a drain 12 for PTFT.
[0025]
In addition, when aluminum (Al) is used as the gate electrode material, it is possible to apply the self-line method by anodizing the surface after patterning with the second photomask (2). Since the source / drain contact holes can be formed closer to the gate, the TFT characteristics can be further improved by reducing the mobility and the threshold voltage.
[0026]
These were performed through the gate insulating film 54. However, in FIG. 6B, the silicon oxide on the silicon film may be removed using the gate electrodes 21 and 9 as a mask, and then boron and phosphorus may be directly implanted into the silicon film.
[0027]
Next, heating annealing was performed again at 600 ° C. for 10 to 50 hours. PTFT source 10 and drain 12, NTFT source 18 and drain 20 were fabricated as P ⁺ and N ⁺ by activating impurities. Channel formation regions 19 and 11 are formed as semi-amorphous semiconductors under the gate electrodes 21 and 9.
[0028]
In this way, a C / TFT can be made without applying a temperature in all steps to 700 ° C. or higher even though it is a self-alignment method. Therefore, it is not necessary to use an expensive substrate such as quartz as the substrate material, and this process is extremely suitable for the large-pixel liquid crystal display device of the present invention.
[0029]
In this example, thermal annealing was performed twice in FIGS. 6 (A) and 6 (D). However, the annealing shown in FIG. 6A may be omitted depending on the required characteristics, and both may be used as the annealing shown in FIG. 6D to shorten the manufacturing time. In FIG. 6E, an interlayer insulator 65 is formed as a silicon oxide film by the sputtering method described above. The silicon oxide film may be formed by LPCVD, photo CVD, or atmospheric pressure CVD. For example, the electrode window 66 is formed to have a thickness of 0.2 to 0.6 μm, and then the electrode window 66 is formed using the photomask (5). Further, aluminum is formed on the entire surface by sputtering, and the leads 71 and 72 and the contacts 67 and 68 are prepared using a photomask (6), and then the surface is planarized with an organic resin 69 such as translucent polyimide. Resin was applied and formed, and electrode drilling was performed again with a photomask (7).
[0030]
As shown in FIG. 6 (F), two TFTs have a complementary structure, and the output end thereof is connected to the electrode of one pixel of the liquid crystal device as a transparent electrode, so that ITO (indium tin oxide) is formed by sputtering. Film). This was etched with a photomask (8) to form an electrode 17. This ITO was formed at room temperature to 150 ° C., and was achieved by oxygen at 200 to 400 ° C. or annealing in the atmosphere. Thus, PTFT 13, NTFT 22, and transparent conductive film electrode 17 were fabricated on the same glass substrate 50. The obtained TFT has PTFT mobility of 20 (cm ² / Vs), Vth of −5.9 (V), NTFT mobility of 40 (cm ² / Vs), and Vth of 5 0.0 (V).
[0031]
A transparent electrode is provided on the entire surface of one substrate and the other glass substrate for a liquid crystal device manufactured according to the method as described above, and these substrates are bonded together to form a liquid crystal cell, and a TN liquid crystal material is injected therein. . FIG. 5 shows the arrangement of electrodes and the like of this liquid crystal display device. PTFT 13 is provided at the intersection of first signal line 5 and third signal line 3, and PTFTs for other pixels are similarly provided at the intersection of first signal line 5 and third signal line 4. Is provided. On the other hand, the NTFT is provided at the intersection of the second signal line 8 and the third signal line 3. In addition, PTFTs for other pixels are provided at the intersections between the other adjacent first signal lines 6 and the third signal lines 3, and the first signal lines 6 and the third signal lines 6 are similarly provided. PTFT is provided at the intersection with the signal line 4. A matrix configuration using such a C / TFT was provided. The PTFT 13 is connected to the first signal line 5 through a contact at the input end of the drain 10, and the gate 9 is connected to the signal line 3 in which a multilayer wiring is formed. The output terminal of the source 12 is connected to the electrode 17 of the pixel through a contact.
[0032]
On the other hand, the input terminal of the drain 20 is connected to the second signal line 8 through a contact, the NTFT 22 is connected to the signal line 3, the output terminal of the source 18 is connected to the pixel electrode through the contact in the same manner as the PTFT. 17 is connected. Further, other C / TFTs connected to the same third signal line and adjacent thereto have PTFT 13 connected to first signal line 6 and NTFT 22 connected to second signal line 7. Thus, between the pair of signal lines 5 and 8 (inside), one pixel was constituted by the pixel 23 made of a transparent conductive film and the C / TFT. By repeating this structure left and right and up and down, a liquid crystal display device having a large pixel size of 640 × 480 and 1280 × 960 can be obtained by enlarging the 2 × 2 matrix.
[0033]
The feature here is that the pixel electrode 17 is fixed to three values of the liquid crystal potential V _LC by providing two TFTs in a complementary configuration in one pixel.
[0034]
Further, PTFTs are adjacent to each other, and the potential difference applied between the signal lines connected to the PTFT is the maximum V _SS , so that there is little leakage.
[0035]
Next, as a second substrate, ITO (indium tin oxide film) was formed by sputtering on a blue plate glass on a substrate in which 2000 mm of silicon oxide film was laminated. This ITO was formed at room temperature to 150 ° C., and was achieved by oxygen at 200 to 400 ° C. or annealing in the atmosphere.
[0036]
On the said board | substrate, the polyimide precursor was printed using the offset method, and it baked at 350 degreeC for 1 hour in non-oxidizing atmosphere, for example, nitrogen. Thereafter, a known rubbing method was used to modify the polyimide surface, and at least in the initial stage, means for aligning liquid crystal molecules in a certain direction was provided to form a second substrate.
[0037]
Thereafter, a liquid crystal composition exhibiting ferroelectricity was sandwiched between the first substrate and the second substrate, and the periphery was fixed with an epoxy adhesive. A TAB-shaped drive IC was connected to the lead on the substrate, and a polarizing plate was attached to the outside to obtain a transmissive liquid crystal display device.
[0038]
FIG. 7 shows how pixels A, E, and C are displayed when the drive waveforms shown in FIG. 4 are added. This figure shows that the larger the number of dots, the darker the screen, and it was found that sufficiently clear gradation display can be obtained.
[0039]
Example 2 In this example, a first substrate and a second substrate were obtained by the same process as in Example 1. However, no polyimide alignment film was formed on the second substrate. Since the video camera is used as a viewfinder for a video camera, the pixel pitch is set to 60 μm and a matrix configuration of 200 × vertical 300 × horizontal is used.
[0040]
In this embodiment, a dispersion type liquid crystal display device in which a nematic liquid crystal composition is dispersed in an acrylic organic resin as the liquid crystal composition is used. After 62% by weight of nematic liquid crystal is dispersed in an epoxy-modified acrylic resin having ultraviolet curing properties and sandwiched between the first substrate and the second substrate, a UV light source having an output of 1000 mW is cured by irradiation for 20 seconds. It was.
[0041]
With the number of time divisions for gradation display being 16, a liquid crystal display device capable of displaying a total of 4096 colors in 16 tones for each color. The drive waveform at that time is shown in FIG.
[0042]
Conventionally, as a method of performing gradation display, there has been proposed a method of performing gradation display according to the ON / OFF ratio using, for example, 16 frames using a plurality of writing (display frames). In this case, when 16 frames are turned on and 8 frames are turned off, and the remaining 8 frames are turned off, gradation display is performed with an average transmittance of 50%. In addition, when 4 frames of the 16 frames are ON and the remaining 12 frames are OFF, gradation display is performed with an average transmittance of 25% transmission. However, when this method is used, there is a high possibility of interrupting the minimum number of confirmation frames corresponding to 30 frames, which is a frame that cannot be confirmed by human eyes, and this has been a factor that deteriorates display quality.
[0043]
However, in the present invention, in the method according to the present invention in which gradation display is performed by increasing the driving frequency of the driver, the gradation confirmation can be performed without reducing the substantial frame frequency. Therefore, it was possible to provide a high-quality screen that does not cause deterioration in display quality.
[0044]
By using the same process and driving method, a word processor screen, a computer screen, a projection-type video display device, and the like can be created.
[0045]
【The invention's effect】
The gradation display of the display device using the display driving method having the display timing related to the unit time t for writing to an arbitrary pixel and the time F for writing one screen is performed without the time F being deflected. By making the signal during the writing time time-division, it is possible to obtain a clear gradation display that is digitally controlled, and according to the division ratio without image quality degradation due to a decrease in the frame frequency defined by the time F. The gray scale can be displayed.
[Brief description of the drawings]
1 is a drive waveform according to an example of the present invention. FIG. 2 is a diagram showing an electro-optical characteristic of a nematic liquid crystal. FIG. 3 is an inverter type CTFT matrix circuit diagram. FIG. 4 is a drive waveform of a conventional example. FIG. 6 is a plan view of the display device. FIG. 6 is a process according to the present embodiment. FIG. 7 is a display example according to the present embodiment.

Claims (5)

A thin film transistor formed on an insulating surface;
An organic resin film formed on the thin film transistor;
A wiring formed on the organic resin film and electrically connected to the thin film transistor through a hole formed in the organic resin film;
A display device, wherein the gate insulating film of the thin film transistor is a silicon oxide film containing fluorine. A thin film transistor formed on an insulating surface;
An organic resin film formed on the thin film transistor;
A wiring formed on the organic resin film and electrically connected to the thin film transistor through a hole formed in the organic resin film;
A driving IC electrically connected to the wiring using a TAB tape;
A display device, wherein the gate insulating film of the thin film transistor is a silicon oxide film containing fluorine. 3. The display device according to claim 1, wherein the display device is a projection-type video display device. A computer comprising the display device according to claim 1. A viewfinder comprising the display device according to claim 1.

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